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The bioavailable phosphorus (P) released from sediments is the major source of marine dissolved phosphorus (P). Different P forms such as LSor-P, Fe-P, CFA-P and Org-P can release from sediments to seawater as bioavailable P. Opal-associated P (Opal-P) was recently reported to release to seawater, enhancing the amount of P in seawater. So Opal-P also belongs to bioavailable P. However, little studies have been reported about Opal-P in the East China Sea (ECS), leading the bioavailable P in seawater has been underestimated in ECS. This study investigated seven different P reservoirs (Lsor-P, Fe-P, CFA-P, Detr-P, Org-P, Opal-P and Ref-P) using SEDEX and TP, TIP, TOP. Surface samples were collected from the Changjiang estuary and south of Cheju Island in the ECS, and core sediments were collected from southwest of Cheju Island. For surface sediments, the concentrations of most P forms were higher in stations located in Changjiang estuary than those in stations located in the south of Cheju Island. DOP and Opal-P had the adverse distribution tendency. This distribution pattern might impact by the river and terrestrial input based on the positive relationship of the ratio of clay and the concentration of CFA-DIP and CFA-TP. For core sediments, TIP was the most important form of TP. TP, TIP and TOP had different profiles. In up layer (<20cm), TP and TIP remained stable, and TOP increased with depth. It may reflect that different fractions interconverted at first 20cm or the source of particles loaded P changed. In low parts (>20cm), TP, TIP and TOP were all decreased with depth. The concentration of Opal-P had no distinct variation with depth with a range 0.6-1.4μmol g^-1. The concentration of bioavailable P (the sum of LSor-P, Fe-P, CFA-P, Org-P, Opal-P) is 9.6-13.5 μmol g^-1 in which Opal-P was 0.6-2.3μmol g^-1, occupied 5-20% of bioavailable P. Therefore, Opal-P should be included when measured bioavailable P as Opal-P accounts a big portion in bioavailable P. Moreover, the burial flux of Opal-P and bioavailable P are about 0.4-20.0×10¹⁰ mol yr^-1 and 0.2-34.0×10⁹ mol yr^-1, respectively (the rate of mass accumulation and area of ECS is 0.05->2 g cm^-2 yr^-1 and 0.74×10⁶ km²). Acknowledgements：This study was financially supported by the National Nature Science Foundation of China (No. 41276071, 41530965).